A water-absorbent resin has been widely used in various fields such as hygienic materials such as disposable diaper and sanitary napkin; horticultural materials such as water-retaining materials for soil and soil improvers; and industrial and construction materials such as water blocking materials for cables and dewfall preventing materials.
As the water-absorbent resin, there have been known, for instance, hydrolysates of starch-acrylonitrile graftcopolymers (Japanese Examined Patent Publication No. Sho 49-43395), neutralized starch-acrylic acid salt graftcopolymers (Japanese Patent Laid-Open No. Sho 51-125468), saponified vinyl acetate-acrylic ester copolymers (Japanese Patent Laid-Open No. Sho 52-14689), partially neutralized polyacrylic acid (Japanese Patent Laid-Open No. Sho 62-172006), and the like.
Properties desired for water-absorbent resins include a large amount of water absorption, high water absorption rate, high swellability, optimal particle diameter suitable for its uses and the like. Especially, in the resin for water blocking materials for cables, a water-absorbent resin particle having a large amount of water absorption and high swellability, and being small in a particle diameter has been desired. However, it is difficult to enhance these properties at the same time.